In a production environment, capacity planning generally refers to the process of predicting future needs for production resources such as machines, labor, and raw materials. Capacity planning can be used to assess whether the production capabilites of a particular production facility are sufficient for executing a Master Production Schedule (MPS), which, if determined to be feasible, may become the input to a Material Requirement Plan (MRP). An MPS is a schedule for processing one or more items for purposes of meeting a demand. For example, an MPS may specify a number of products that should be manufactured on a weekly basis for the next month to meet projected consumer demand. An MRP is a set of requirements for materials which are necessary in order to meet an MPS. For example, an MRP may list the quantity of all components and materials required to fabricate items according to the MPS and the date that the components and materials are required.
Capacity planning is typically performed in stages. Different stages of planning have different objectives and may consider different factors. For example, different time frames may be considered in different stages. A rough long-term plan can be first put in place and then mid- to short-term plans can be implemented accordingly as time progresses. The long-term planning is often referred to as rough-cut capacity planning (RCCP).
Traditionally, the general goal in RCCP is to balance the total available capacity (i.e. the manufacturing capability of a production facility) with the total required capacity demanded by the MPS. What is meant by “balance” is that an attempt is made to match required capacity with available capacity. Insufficient available capacity of a production facility would obviously result in an inability to fulfil the MPS. In this case the user may decide either to increase available capacity or, if possible, to adjust the MPS to reduce required capacity. Excess available capacity would waste resources. In this case, the user may decide to decrease available capacity or adjust the MPS to increase required capacity.
Before considering known RCCP approaches, it is helpful to review basic manufacturing terminology. When a batch of items is to be processed, the processing is typically governed by a “work order”. As is known in the art, a work order (also referred to as a “job” or a “lot”) describes a set of operations (e.g. cutting, sanding, painting) that is to be performed to process a particular item. Processing may for example comprise the steps necessary for generating a product from raw materials or components. A work order typically includes a due date, i.e., a time by which completion of the work order is needed. A “work center” is a set of one or more machines having similar capabilities on which a particular operation can be completed. For example, in a semiconductor backend assembly environment, a “Wire Bond” work center may contain multiple wire bonders which come from different equipment manufacturers, yet they are all generally capable of completing the wire bonding operation. The terms “work center” and “operation” are sometimes used interchangeably. The term “items” and the term “products” may be used interchangeably herein to refer to units to be processed.
In known RCCP approaches, available capacity C_Availk at a particular work center k is typically estimated using the following formula:C_Availk=TkUkEk 
Tk refers to the total number of machine hours available at work center k for a chosen planning period or “time horizon” (e.g. a week). Uk refers to the machine utilization ratio for the work center, which is the ratio between total actual operational hours and total available hours. Ek refers to the efficiency of the machines comprising the work center. Ek may be determined by dividing Standard Hours by Hours Work and multiplying by 100. “Standard Hours” refers to the length of time that should be required to set up a given machine or operation and run one item (e.g. a part) through that operation. Uk and Ek are typically estimated for the work center k using historical data.
For example, if a work center k is composed of four machines staffed for two eight-hour shifts, five days a week, then there are 320 total hours of machine time available per week (i.e. Tk=320 hours/week). If the operation's machine utilization (Uk) and efficiency (Ek) are 90% and 95% respectively based on historical statistical data, then the available capacity for the work center (estimated) for one week would be:C_Availk=320 hours/week*90%*95%=273.6 hours/week
This calculation may be repeated for each work center in a production facility, and the smallest value for any work center in the production facility may be used as an estimate of the available capacity for the production facility as a whole.
Obviously, the estimated available capacity as computed above is a very rough figure, in the sense that is based on average historical data. As well, this figure assumes that machines are available throughout their shifts and does not account for any product-specific factors which may exist, such as production constraints or bottlenecks. A bottleneck is a resource whose capacity is less than the demand placed upon it. For example, a bottleneck machine or work center exists where jobs are processed at a slower rate than they are demanded.
There are a number of known approaches to calculating the required capacity. Typical approaches include the Capacity Planning using Overall Factors (CPOF), Bill of Resource (BoR) (also known as Bill of Labor), and Resource Profile approaches.
In the CPOF approach, the total required capacity C_Reqt for all products to be processed according to an MPS during a particular time period (i.e. time interval) is calculated as follows:C_Reqt=Σ(Di*ti)
where Di is the number of units of a particular product i to be produced, ti is the number of working hours (at one or more work centers) required to process one unit of product i, and wherein the summation is performed for each different product i to be produced.
For example, assume that the master production schedule is as shown in Table 1:
TABLE 1Master Production Schedule for Time periods T1, T2, and T3T1T2T3Product X 50,000 units 60,000 units80,000 unitsProduct Y100,000 units120,000 units80,000 units
The above MPS indicates that, e.g., during time period T1, which may be a week for example, it is desired to produce 50,000 units of Product X and 100,000 units of product Y.
If the time required to produce products X and Y is as shown in Table 2:
TABLE 2Time Required to Produce Products X and YTime required to manufactureProduct(based on historical data)Product X1 hour/1000 unitsProduct Y2 hours/1000 units
Based on the above, the total (production facility-wide) capacity C_Reqt required for all products to be produced during, say, time period T1, would be as follows:
                                             C_Req            t                    =                    ⁢                                    (                              50                ,                000                ⁢                                                                  ⁢                units                *                1                ⁢                                                                  ⁢                                  hour                  /                  1000                                ⁢                                                                  ⁢                units                            )                        +                                                                  ⁢                      (                          100              ,              000              ⁢                                                          ⁢              units              *              2              ⁢                                                          ⁢                              hours                /                1000                            ⁢                                                          ⁢              units                        )                                                        =                    ⁢                                    50              ⁢                                                          ⁢              hours                        +                          200              ⁢                                                          ⁢              hours                                                                    =                    ⁢                      250            ⁢                                                  ⁢            hours                              
Similar calculations would yield C_Reqt values of 300 hours and 240 hours for time periods T2 and T3 respectively.
To estimate the required capacity C_Reqk at an individual work center k for a given time period, the total workload C_Reqt for the time period is prorated across work centers using historical workload distribution data. For example, if historical data indicates that, on average, 60% of the time required to manufacture a product (any product) at the production facility in question is spent at a first work center ST1 and the remaining 40% of the time required to manufacture the product is spent at a second work center ST1, then the required capacity at a work center C_Reqk may be determined as shown in Table 3:
TABLE 3Capacity Required at Work Centers ST1 and ST2 forDifferent Time Periods T1, T2 and T3T1T2T3Capacity250 hours *300 hours *240 hours *required60% = 150 hours60% = 180 hours60% = 144 hoursat workcenter ST1(C_ReqST1)Capacity250 hours *300 hours *240 hours *required40% = 100 hours40% = 120 hours40% = 96 hoursat workcenterST2(C_ReqST2)
Thereafter, for each work center k, the required capacity C—Reqk may then be compared against available capacity C_Availk in order to assess whether the MPS is feasible.
The CPOF approach is straightforward. However, this approach does not take into account job-specific factors which may impact negatively upon the accuracy of RCCP. For example, if current product mixes differ from the historical product mixes upon which the “60%-40%” historical workload distribution across work centers is based, required capacity calculated using the CPOF approach may not truly reflect required capacity for the current product mix. The CPOF approach also fails to consider lead-time offsets.
In the BoR approach, it is not assumed that the workload distribution across work centers for a current product mix will necessarily match average historical workload distribution across work centers. Rather, the workload distribution is estimated on a product-by-product basis for each product in the MPS. That is, for each product in the current mix, and for each work center/operation k involved in processing said product, the required capacity C_Reqk for completing the operation is calculated using the following formula:C_Reqk=Σ(Di×Lik)
where Di is the quantity of product i to be produced, Lik is the processing rate (e.g. expressed in hours/unit) at work center k for product i, and wherein the summation is performed for each different product i to be processed. This approach takes routing of specific product mixes into consideration.
For example, assuming a master production schedule as shown in Table 1 above and product routings as shown in Table 4:
TABLE 4Product RoutingsFirst operationSecond operationProduct XST1ST2Product YST1ST2
and further assuming that the time required to complete operations ST1 an ST2 for products X and Y is as shown in Table 5:
TABLE 5Time Required to Complete Operations ST1 and ST2 forProducts X and YProduct XProduct YOperation ST10.5 hours/1000 units1.4 hours/1000 unitsOperation ST20.5 hours/1000 units0.6 hours/1000 units
then the required capacity C_Reqk at a work center k may be determined as shown in Table 6:
TABLE 6Capacity Required at Work Centers ST1 and ST2 for Different Time Periods T1, T2 and T3T1T2T3Capacity required50,000 units of60,000 units of80,000 units ofat work center ST1product X * 0.5product X * 0.5product X * 0.5(C_ReqST1)hours/1000 units + 100,000hours/1000 units + 120,000hours/1000 units + 80,000units ofunits ofunits ofproduct Y * 1.4product Y * 1.4product Y * 1.4hours/1000 units = 165hours/1000 units = 198hours/1000 units = 152hourshourshoursCapacity required50,000 units of60,000 units of80,000 units ofat work center ST2product X * 0.5product X * 0.5product X * 0.5(C_ReqST2)hours/1000 units + 100,000hours/1000 units + 120,000hours/1000 units + 80,000units ofunits ofunits ofproduct Y * 0.6product Y * 0.6product Y * 0.6hours/1000 units = 85hours/1000 units = 102hours/1000 units = 88hourshourshours
Disadvantageously, however, the BoR approach does not consider lead-time offsets.
In the Resource Profile approach, lead-time offsets are taken into account. Each bill of resource is time-phased. For instance, when two operations A and B need to be completed but operation B can only be performed after operation A is completed, operation B will have a lead-time equaling the time required to complete the operation A.
For example, assuming that the time required to complete operations ST1 and ST2 for product X is as shown in the time-phased BoR illustrated in Table 7:
TABLE 7Time Required to Complete Operations ST1 and ST2 for Product XT-1TOperation ST10.5 hours/1000 unitsOperation ST20.5 hours/1000 units
and assuming that the time required to complete operations ST1 and ST2 for product Y is as shown in Table 8:
TABLE 8Time Required to Complete Operations ST1 and ST2 for Product YT-1TOperation ST11.4 hours/1000 unitsOperation ST20.6 hours/1000 units
then the required capacity at work centers ST1 and ST2 for processing product X to execute the MPS of Table 1 would be as shown in Table 9:
TABLE 9Capacity Required at Work Centers ST1 and ST2 for Producing Product XT1-1T1T2T3Capacity50,000 units of60,000 units of80,000 units ofrequired atproduct X * 0.5product X * 0.5product X * 0.5work centerhours/1000hours/1000hours/1000ST1units = 25units = 30units = 40(C_ReqST1)hourshourshoursCapacity50,000 units of60,000 units of80,000 units ofrequired atproduct X * 0.5product X * 0.5product X * 0.5 hours/1000work centerhours/1000hours/1000units = 40 hoursST2units = 25units = 30(C_ReqST2)hourshours
and the required capacity at work centers ST1 and ST2 for processing product Y according to the MPS of Table 1 would be as shown in Table 10:
TABLE 10Capacity Required at Work Centers ST1 and ST2 for Producing Product YT1-1T1T2T3Capacity100,000 units of120,000 units of80,000 units ofrequired atproduct Y * 1.4product Y * 1.4product Y * 1.4work centerhours/1000hours/1000hours/1000ST1units = 145units = 168units = 112(C_ReqST1)hourshourshoursCapacity100,000 units of120,000 units of80,000 units ofrequired atproduct Y * 0.6product Y * 0.6product Y * 0.6work centerhours/1000hours/1000hours/1000ST2units = 60units = 72units = 48(C_ReqST2)hourshourshours
The total required capacity at work centers ST1 and ST2 for processing products X and Y would thus be as shown in Table 11:
TABLE 11Capacity Required at Work Centers ST1 and ST2 for Producing Products X and YT1-1T1T2T3Capacity required at25 hours + 14030 hours + 6840 hours + 112work center ST1hours = 165hours = 198hours = 152(C_ReqST1)hourshourshoursCapacity required at25 hours + 6030 hours + 7240 hours + 48work center ST2hours = 85hours = 102hours = 88(C_ReqST2)hourshourshours
The RCCP approaches described above are generally simple to implement and use but they, and other known approaches, have a drawback in that the estimated capacities (both available and required) may not be sufficiently accurate, such that non-feasible production plans may result. For instance, while the rough-cut capacity plan indicates sufficient capacity, short-term capacity shortfalls may still arise. While some degree of discrepancy between a rough-cut capacity plan and a short-term plan may be expected, it is desirable to limit the discrepancy as much as possible.
It is therefore desirable to provide more accurate, feasible and practical RCCP.